a bowl-shaped opening at the top of a volcano

A well-defined circular depression formed by the explosive eruption of volcanic rock.

A steep, bowl-shaped depression surrounding a vent. A volcanic crater forms when the walls of a vent collapse inward following an eruption.

a steep-walled depression at the top or on the flank of a volcanic cone, out of which the volcanic materials are ejected

Perhaps the most conspicuous part of a volcano is the crater, a basin of a roughly circular form within which occurs a vent (or vents) from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of vast depth. Very large features of this sort are termed calderas.